gphil,

That's a pretty standard aileron installation for ARFs and the aileron control arm should stick out the bottom of the wing. If I understand your question correctly, the answer is it depends (and really doesn't matter much). Orienting the servo so that the arm is further towards the rear of the plane results in a slightly shorter (and therefore more rigid) control rod installation, a good thing. However, before attaching the servo to the cover, move the arm through its full range of motion (+/- 60 degrees or so) and make sure the slot in the cover is long enough so that arm does not hit it. If so, you can either turn the servo over so the arm is further toward the front of the plane or possibly lenghten the slot so that there is no interference.

Tony